From mboxrd@z Thu Jan  1 00:00:00 1970
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Subject: Re: [PATCHv2 3/9] v4l: add buffer exporting via dmabuf
Date: Tue, 31 Jul 2012 18:28:12 +0200
Message-ID: <26877422.izWOc7eKQo@avalon>
References: <1339684349-28882-1-git-send-email-t.stanislaws@samsung.com> <36319543.mdnBULUSen@avalon> <201207311639.02693.remi@remlab.net>
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To: =?ISO-8859-1?Q?R=E9mi?= Denis-Courmont <remi@remlab.net>
Cc: Hans Verkuil <hverkuil@xs4all.nl>, Tomasz Stanislawski <t.stanislaws@samsung.com>, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, airlied@redhat.com, m.szyprowski@samsung.com, kyungmin.park@samsung.com, sumit.semwal@ti.com, daeinki@gmail.com, daniel.vetter@ffwll.ch, robdclark@gmail.com, pawel@osciak.com, linaro-mm-sig@lists.linaro.org, subashrp@gmail.com, mchehab@redhat.com, g.liakhovetski@gmx.de
List-Id: dri-devel@lists.freedesktop.org

Hi R=E9mi,

On Tuesday 31 July 2012 16:39:00 R=E9mi Denis-Courmont wrote:
> Le mardi 31 juillet 2012 14:56:14 Laurent Pinchart, vous avez =E9crit=
 :
> > > For that matter, wouldn't it be useful to support exporting a use=
rptr
> > > buffer at some point in the future?
> >=20
> > Shouldn't USERPTR usage be discouraged once we get dma-buf support =
?
>=20
> USERPTR, where available, is currently the only way to perform zero-c=
opy
> from kernel to userspace. READWRITE does not support zero-copy at all=
=2E MMAP
> only supports zero-copy if userspace knows a boundary on the number o=
f
> concurrent buffers *and* the device can deal with that number of buff=
ers;
> in general, MMAP requires memory copying.

Could you please share your use case(s) with us ?

> I am not sure DMABUF even supports transmitting data efficiently to
> userspace. In my understanding, it's meant for transmitting data betw=
een
> DSP's bypassing userspace entirely, in other words the exact opposite=
 of
> what USERBUF does.

--=20
Regards,

Laurent Pinchart